Oxidized bitumen (bitumen is also referred to as asphalt) is used by the roofing industry to make roofing shingles and roofing membranes, among other things. Oxidized bitumen, also called “blown coating,” is generally produced by oxidizing a suitable feedstock bitumen, usually straight run bitumen or blends of straight run bitumen, by blowing an oxygen-containing gas (e.g., air, oxygen or an oxygen-inert gas mixture) through the bitumen feedstock at an elevated temperature (usually between 230° C.-290° C. (450° F.-550° F.)) for a certain amount of time (which can be more than 10 hours). Sometimes, this process is conducted in the presence of one or more catalysts. As a result of blowing oxygen, or oxygen-containing gas, through bitumen, the bitumen's properties change. Generally, the blowing process is terminated once the bitumen has obtained the desired penetration, softening point and viscosity.
While the above described process is widely used in the industry, it has significant shortcomings. For example, the process is time consuming and the amount of energy needed for it to work is high because the process must be conducted at a temperature at which the feedstock is fluid enough to allow oxygen-containing gas to bubble through it. More importantly, the bitumen fumes produced by heating the feedstock and blowing an oxygen-containing gas through it are considered a health hazard and are potentially carcinogenic. Examples of compounds in these bitumen fumes include hydrogen sulfide, sulfur oxides (SOx), organosulfur compounds, hydrocarbons, nitrogen oxides (NOx) and carbon monoxides.
Prior to their release into the atmosphere, the bitumen fumes created by the described blowing process are often passed through a water-sealed knockout tank and then subjected to an incineration process to reduce the emission of hazardous substances. However, these emission control measures are expensive and they usually do not prevent the emission of all potentially hazardous substances.
Roofing flux feedstocks require stringent properties to ensure that the resulting blown coating has properties meeting its specifications. Roofing flux feedstocks are in limited supply.
Thus, there remains a need to develop a method that does not rely on the described blowing process but that nevertheless results in bitumen compositions that have the properties of oxidized bitumen. The present invention addresses this need.